The first order of business...
The first order of business when it arrived at Willy's Carb & Dyno Shop was to bolt it onto one of the company's 400ci test mules and spin it up on the dyno to get a baseline.
The first step upon arrival at Willy's is a session on top of one of the shop's three 400ci dyno engines hooked up to a Superflow SF-902 x-dynamometer to see how it's metered right from the start. This is an important part of the diagnosis-why go to greater expense than you need to if a carb only needs some minor adjustment? "If it was calibrated well and then it doesn't run properly, we know what we need to do," Krup says. "Or it could just be that the jetting or the air bleeds aren't right. A lot of times you can just go in and correct that kind of stuff and help the carb out quite a bit without spending a lot of money on it. It also gives us a guideline so when somebody sends us something we know how much power they're picking up when they get it back. You can almost grade their happiness off that before they even get it."
Into the tumbler it goes for...
Into the tumbler it goes for 45 minutes of gentle vibration to further smooth and renew the surfaces.
After a pull or two on the dyno, the carburetor is then stripped completely down to its component parts so the work can begin in earnest. First up is a session on the bench with hand deburring and chamfering done before the carb body, bowls, and throttle plate are sent to spend about 45 minutes in a vibrating tank filled with glass beads. Glass beading the carb will also help debur some of the stuff and will take the finish off the carb to give it a whole new cosmetic look-it comes out of the tank looking like freshly-cast alloy.
The choke horn is milled away...
The choke horn is milled away since the carb's new life won't involve the use of the choke and because this helps flow more directly into the venturis.
After the application of a new dichromate finish to inhibit corrosion, the next step is to mill all the gasket mating surfaces on the main body so they're true and flat to ensure good internal sealing as well as to curb any external leakage. The choke horn can also be removed at this point. "With a new carb, you're relying on Holley's mold to provide gasket mating surfaces that are flat and true," Krup says. "I promise you that they're not straight and true right out of the Holley box. We usually take off between 0.025- to 0.030-inch to clean them up."
Getting all those gasket surfaces flat and true so there's no surface leakage at all is the key to getting a carburetor to perform correctly. Krup says, "there is all sorts of circuit bleeding on a factory carburetor. You always hear the story, 'I got this new carburetor and it ran good for a while, but a month later I had to start moving the idle mixtures around, and they won't stay adjusted.' The gaskets are temporarily sealing the circuits, but then they start bleeding because you're trying to seal something up that's not flat and true. So some of the fuel from the idle circuit goes over into the transfer or power circuit-it'll just constantly be bleeding from one circuit to another, and the thing will never run right."
Disassembly is as thorough...
Disassembly is as thorough as you can get without splitting atoms. Every part and piece is checked and evaluated.
The old throttle shaft bushings...
The old throttle shaft bushings are removed, and the throttle body is reamed for new ones.
Next, the throttle body is...
Next, the throttle body is blasted by hand to remove any crud, as well as to give the metal some "tooth" for a new finish to come later.